Metals Phlogiston theory

This definition was as accurate a definition as the knowledge of the time permitted and was indeed the same as given by Lavoisier and by later chemists until the development of the phenomena of radioactivity afforded a more intimate concept of the nature of the element. Neither Boyle nor his contemporaries ventured to assert that any known substance was such an element, and the subsequent rise and acceptance of the Phlogiston Theory tended to postpone any recognition of the elementary character of even such metals as gold or silver, until that theory was abandoned. 

As to the real nature of fixed air, Black, in his manuscript notes, says With regard to its origin, when treating of inflammable substances and metals, I shall consider this more completely. I shall now only hint that it is a vital air, changed by some matter, seemingly the principle of inflammability, [that is phlogiston].6 A contemporary of Black, Dr. Leslie, also says, Dr. Black seems to consider fixed air as a particular modification of common air with the principle of inflammability. 0 Black was an adherent of the phlogiston theory until after Lavoisier had published, in 1789, his Elementary... 

My father says, I believe there is something in this phlogiston theory that may shed all kinds of light on the behavior of metals when heated or burned. We will next try the same experiment on sulfur, iron, and lead. Make a list. He pulls off his wig, throws it on the bench, puts it back on his head. 

A precise algebra of weight and heat he wished to implement on chemical processes still eluded him, however, if metals contained an unspecified amount of fire or phlogiston. He could not rationally maintain the theory that bodies could assume different forms depending on their fire content if both solid metals and fluid airs could retain an excess quantity of fire or phlogiston. That is, he could no longer endorse the phlogiston theory and the fixation of air simultaneously, as he previously had. 

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